Fluid compositions for dual clutch transmissions

ABSTRACT

An additive composition and lubricating fluid are disclosed that provide high steel-on-paper friction durability, good metal-metal extreme pressure performance characteristics and synchronizer performance. The lubricating fluid includes a base oil, a succinimide dispersant, a succinimide friction modifier, and a phosphonate. Also disclosed is a method for lubricating a dual clutch transmission employing a plurality of wet clutches, with the lubricating fluid of the disclosure.

BACKGROUND

1. Field

The present disclosure relates to a lubricant and a method forlubricating an automated dual clutch transmission having a plurality ofwet clutches.

2. Brief Description of the Prior Art

Dual clutch transmissions, also known as double clutch or twin clutchtransmissions, of a variety of types are known. Dual clutchtransmissions are known to employ either dry or wet clutches. Some dualclutch transmissions employing wet clutches include hydrodynamic torqueconverters. For example, European publication EP 1 052 421 A, Nov. 15,2000, discloses a multiple clutch system for a transmission, with twomulti-disk clutches that are coaxial with each other, and each clutch isassigned to one of two shafts. The two clutches are arranged in a sealedchamber, which contains lubricating oil.

Volkswagen, for example, has introduced an automated dual clutchtransmission (DCT) in Europe. Progressive improvements in the design andperformance of automatic transmission and wet brake systems, and otherfriction-depending lubricants, requires concomitant progressiveimprovements in the design and performance of automatic transmissionfluids, fluids for wet brake systems, and additive packages(concentrates) used in the formulation of automatic transmission fluidsand wet brake fluids.

DCT's have an automatic direct-shifting gearbox (DSG) provided with anintegrated dual clutch. These DCT's are designed to provide better fueleconomy. However, these DCT's differ from automated manual transmissionssince the DCT's typically do not include a torque converter. Instead,coordination of manual transmission gears is achieved through the use ofdual wet clutches. As a result, performance requirements for fluids forlubricating DCT's involve elements of both manual transmissionlubricants, and elements of automatic transmission lubricants. One ormore of synchronization, extreme pressure performance, steel-on-steelfriction material performance and steel-on-paper friction durability maybe important for these DCT's.

Published European patent application publication number EP 0 020 037discloses a lubricating oil composition containing a friction-reducingamount of an additive selected from the group consisting of oil solublealiphatic hydrocarbon-substituted succinimide and succinamide andmixtures thereof wherein said hydrocarbon substituent contains about 12to 36 carbon atoms. Similar friction modifiers are disclosed for use inautomatic transmission fluids in U.S. Pat. Nos. 5,171,466; 5,312,555;5,328,619; 5,358,652; 5,464,549; 5,505,868; 5,652,201; and 5,817,605.

The use of low molecular weight succinimide friction modifiers made fromamines in automatic transmission fluids is disclosed in U.S. Pat. Nos.5,750,476; 5,811,377; 5,840,662; 5,942,472; 6,225,266; and 6,337,309;and European patent application publication number EP 0 975 714.

The use of phosphonates in various functional fluids such as engine oil,automatic transmission fluids, gear oils, and power transmission fluidsis disclosed in one or more of U.S. Pat. Nos. 4,158,633; 4,325,827; and3,206,401; British patent application publication no. GB 1,247,541 andInternational published patent application nos. WO 98/47989, WO90/09425, and WO 90/09386.

Accordingly, there is a need in the art for improved lubricationcompositions and methods for use in conjunction with automated dualclutch transmissions (DCT's).

SUMMARY OF THE EMBODIMENTS

In a first aspect, the present disclosure relates to an additivecomposition for a transmission fluid for use in automated dual clutchtransmissions. The additive contains at least a dispersant, a frictionmodifier, and a phosphonate. This additive is useful in automatictransmission fluids for meeting the performance requirements for use ofsuch fluids in automated dual clutch transmissions.

In another aspect, the additive composition may be combined with a baseoil to provide an automatic transmission fluid useful for meetingperformance requirements in automated dual clutch transmissions.

In another aspect, the present disclosure relates to a method forincreasing steel-on-steel friction, stabilizing steel-on-steel friction,and/or delivering good synchronizer performance by lubricating atransmission with a lubricating transmission composition including amajor amount of a base oil and an additive composition as describedherein.

In another aspect, the present disclosure relates to a method oflubricating an automated dual clutch transmission with a lubricatingcomposition including a major amount of a base oil and an additivecomposition as described herein.

DETAILED DESCRIPTION

In a first aspect, the present disclosure relates to an additivecomposition for use in transmission fluids. The additive contains atleast a dispersant, a friction modifier and a phosphonate. This additiveis useful in automatic transmission fluids for meeting the performancerequirements for use of such fluids in, for example, dual clutchtransmissions (DCT's). Embodiments of the present disclosure may exhibitimproved steel-on-steel friction as well as steel-on-paper frictionperformance capability, extreme pressure performance, and synchronizerperformance. In particular, the present invention helps to deliver goodsynchronizer performance in synchronization systems employing, forexample, sinter linings or carbon linings which may be used in dualclutch transmission systems.

One advantage of the compositions of the present invention is that thesecompositions are substantially zinc-free. By “substantially zinc-free”is meant that the compositions of the present invention may contain zincas an impurity, and that these compositions are formulated withoutaddition of metallic zinc or zinc compounds, other than zinc or zinccompounds which may be present as a minor impurity in one or more of thecomponents of the compositions of the present invention.

Dispersant

One component of the additive composition of the present disclosure maybe one or more conventional ashless dispersants. Suitable ashlessdispersants are those having basic nitrogen and/or at least one hydroxylgroup in the molecule, such as a succinimide dispersant, a succinamidedispersant, a succinic ester dispersant, a succinic ester-amidedispersant, a Mannich base dispersant, or a hydrocarbyl amine orpolyamine dispersant.

Methods for the production of the foregoing types of ashless dispersantsare known to those skilled in the art and are reported in the patentliterature. For example, the synthesis of various ashless dispersants ofthe foregoing types is described in such patents as U.S. Pat. Nos.2,459,112; 2,962,442, 2,984,550; 3,036,003; 3,163,603; 3,166,516;3,172,892; 3,184,474; 3,202,678; 3,215,707; 3,216,936; 3,219,666;3,236,770; 3,254,025; 3,271,310; 3,272,746; 3,275,554; 3,281,357;3,306,908; 3,311,558; 3,316,177; 3,331,776; 3,340,281; 3,341,542;3,346,493; 3,351,552; 3,355,270; 3,368,972; 3,381,022; 3,399,141;3,413,347; 3,415,750; 3,433,744; 3,438,757; 3,442,808; 3,444,170;3,448,047; 3,448,048; 3,448,049; 3,451,933; 3,454,497; 3,454,555;3,454,607; 3,459,661; 3,461,172; 3,467,668; 3,493,520; 3,501,405;3,522,179; 3,539,633; 3,541,012; 3,542,680; 3,543,678; 3,558,743;3,565,804; 3,567,637; 3,574,101; 3,576,743; 3,586,629; 3,591,598;3,600,372; 3,630,904; 3,632,510; 3,632,511; 3,634,515; 3,649,229;3,697,428; 3,697,574; 3,703,536; 3,704,308; 3,725,277; 3,725,441;3,725,480; 3,726,882; 3,736,357; 3,751,365; 3,756,953; 3,793,202;3,798,165; 3,798,247; 3,803,039; 3,804,763; 3,836,471; 3,862,981;3,936,480; 3,948,800; 3,950,341; 3,957,854; 3,957,855; 3,980,569;3,991,098; 4,071,548; 4,173,540; 4,234,435; 5,137,980; 5,652,201; and Re26,433, herein incorporated by reference. Other suitable dispersants maybe found, for example, in U.S. Pat. Nos. 5,198,133; 5,256,324;5,389,273; and 5,439,606, herein incorporated by reference.

In some embodiments, the ashless dispersant may comprise one or morealkenyl succinimides of an amine having at least one primary amino groupcapable of forming an imide group. The alkenyl succinimides may beformed by conventional methods such as by heating an alkenyl succinicanhydride, acid, acid-ester, acid halide, or lower alkyl ester with anamine containing at least one primary amino group. The alkenyl succinicanhydride may be made readily by heating a mixture of polyolefin andmaleic anhydride to about 180°-220° C. The polyolefin may be a polymeror copolymer of a lower monoolefin such as ethylene, propylene,isobutene, and the like, having a number average molecular weight in therange of about 900 to about 3000 as determined by gel permeationchromatography (GPC).

Amines which may be employed in forming the ashless dispersant includeany that have at least one primary amino group which can react to forman imide group and at least one additional primary or secondary aminogroup and/or at least one hydroxyl group. A few representative examplesare: N-methyl-propanediamine, N-dodecylpropanediamine,N-aminopropyl-piperazine, ethanolamine, N-ethanol-ethylenediamine, andthe like.

Suitable amines may include alkylene polyamines, such as propylenediamine, dipropylene triamine, di-(1,2-butylene)triamine, andtetra-(1,2-propylene)pentamine. A further example includes the ethylenepolyamines which can be depicted by the formula H₂N(CH₂CH₂NH)_(n)H,wherein n may be an integer from about one to about ten. These include:ethylene diamine, diethylene triamine, triethylene tetramine,tetraethylene pentamine, pentaethylene hexamine, and the like, includingmixtures thereof in which case n is the average value of the mixture.These depicted ethylene polyamines have a primary amine group at eachend so they may form mono-alkenylsuccinimides andbis-alkenylsuccinimides. Commercially available ethylene polyaminemixtures may contain minor amounts of branched species and cyclicspecies such as N-aminoethyl piperazine, N,N′-bis(aminoethyl)piperazine,N,N′-bis(piperazinyl)ethane, and like compounds. The commercial mixturesmay have approximate overall compositions falling in the rangecorresponding to diethylene triamine to tetraethylene pentamine. Themolar ratio of polyalkenyl succinic anhydride to polyalkylene polyaminesmay be from about 1:1 to about 2.4:1.

The Mannich base ashless dispersants may be formed by condensing aboutone molar proportion of long chain hydrocarbon-substituted phenol withfrom about 1 to about 2.5 moles of formaldehyde and from about 0.5 toabout 2 moles of polyalkylene polyamine.

In some embodiments, the ashless dispersant may comprise the products ofthe reaction of a polyethylene polyamine, e.g. triethylene tetramine ortetraethylene pentamine, with a hydrocarbon substituted carboxylic acidor anhydride made by reaction of a polyolefin, such as polyisobutene, ofsuitable molecular weight, with an unsaturated polycarboxylic acid oranhydride, e.g., maleic anhydride, maleic acid, fumaric acid, or thelike, including mixtures of two or more such substances.

The dispersant may be present in an amount of from about 1% to about 6%by weight, based on the total weight of the lubricating composition. Asa further example, the dispersant may be present in an amount of about 2wt % to about 4 wt % in the lubricating composition (or finished fluid).The dispersant may be present in an amount of about 10 wt % to about 60wt % in the additive composition.

Boron-Containing Dispersant

In certain embodiments, the additive composition may comprise at leastone boron-containing dispersant, wherein the boron-containing dispersantis free of phosphorus. The boron-containing dispersant may be formed byboronating (borating) an ashless dispersant having basic nitrogen and/orat least one hydroxyl group in the molecule, such as a succinimidedispersant, succinamide dispersant, succinic ester dispersant, succinicester-amide dispersant, Mannich base dispersant, or hydrocarbyl amine orpolyamine dispersant. Methods that can be used for boronating thevarious types of ashless dispersants described above are described inU.S. Pat. Nos. 3,087,936; 3,254,025; 3,281,428; 3,282,955; 3,338,832;3,344,069; 3,533,945; 3,658,836; 3,703,536; 3,718,663; 4,455,243; and4,652,387.

In some embodiments, a boron-containing dispersant may comprise, forexample, a boronated polyisobutylene succinimide or bis-succinimide or amixture thereof. The polyisobutylene may have a molecular weight fromabout 210 to about 1300 amu, as a further example from about 900 to 1300amu, and as an even further example from about 1200 to about 1300 amu.

A boron-containing dispersant may comprise from about 0.1 wt % to about0.7 wt % of boron. As a further example, a boron-containing dispersantmay comprise from about 0.25 wt % to about 0.7 wt % of boron.

Phosphorus-Containing Dispersant

In certain embodiments, the additive composition may comprise at leastone phosphorus-containing dispersant e.g., a phosphorylated dispersant.The phosphorus-containing dispersant may be prepared by phosphorylatingeither a non-boronated dispersant or a boronated dispersant.

When the dispersant contains both phosphorous and boron, the phosphorus-and boron-containing dispersant may comprise, a phosphorylated andboronated polyisobutylene succinimide or bis-succinimide or a mixturethereof. The phosphorus- and boron-containing dispersant may comprise apolyisobutylene having a molecular weight of about 900 amu. Further, thephosphorus- and boron-containing dispersant may comprise the reactionproduct of a polyisobutylene succinimide with a boric acid (i.e.,B(OH)₃) and a phosphorus acid (i.e., H₃PO₃).

The boron and phosphorus may be present in an amount of, for example,about 200 ppm or more of total boron and phosphorus in the lubricatingcomposition (or finished fluid). As a further example, the boron andphosphorus may be present in an amount of, for example, about 400 ppm ormore of total boron and phosphorus in the lubricating composition.

The Friction Modifier

The additive composition and/or lubricating composition may contain afriction-improving amount of a friction modifier, such as an amount thatimproves steel-on-steel friction, steel-on-paper friction, and/orsynchronization performance.

Friction modifiers suitable for use in the present invention includesuch compounds as aliphatic fatty amines or alkoxylated aliphatic fattyamines, alkoxylated aliphatic ether amines, aliphatic carboxylic acids,aliphatic fatty acid amides, alkoxylated aliphatic fatty acid amides,aliphatic fatty imidazolines, and aliphatic fatty tertiary amines,wherein the aliphatic group usually contains above about eight carbonatoms so as to render the compound suitably oil soluble. Also suitableare aliphatic substituted succinimides formed by reacting one or morealiphatic succinic acids or anhydrides with ammonia or other primaryamines such as those taught in EP-A-0389237, as well as mixtures of twoor more friction modifiers. Friction modifiers suitable for use in thepresent invention are described in the following U.S. patents,incorporated herein by reference for their disclosures relating tofriction modifiers: U.S. Pat. Nos. 5,344,579; 5,372,735 and 5,441,656.

A suitable friction modifier may be selected from one or more of oilsoluble aliphatic hydrocarbon-substituted succinimides and mixturesthereof wherein said hydrocarbon substituent contains about 12 to 36carbon atoms. The aliphatic substituent on the succinic group can be anyaliphatic hydrocarbon group containing about 12 to 36 carbon atomsincluding alkyl, alkenyl and polyunsaturated hydrocarbon groups.

Examples of these friction modifiers include:

-   n-dodecynyl succinimide,-   1-methyltridecyl succinimide,-   2-ethyltetradecyl succinimide,-   n-hexadecenyl succinimide,-   n-octadecyl succinimide,-   n-octadecenyl succinimide,-   1-methyleicosyl succinimide,-   n-docosenyl succinimide,-   4-ethyltriacontyl succinimide, and-   n-hexadecenyl succinimide.

In an embodiment, the aliphatic hydrocarbon group may be bonded to thesuccinic group at a secondary carbon atom. These compounds have theformula:

wherein n is a small integer from about 2 to about 4 and Z is the group:

wherein R₁ and R₂ are independently selected from the group consistingof branched and straight chain hydrocarbon groups containing about 1 toabout 34 carbon atoms such that the total number of carbon atoms in R₁and R₂ is about 11 to about 35.

Examples of these friction modifiers are:

-   1-ethyltetradecyl succinimide-   1-methylpentadecenyl succinimide-   1,2-dimethyl octadecenyl succinamide-   1-methyl-3-ethyl dodecenyl succinimide-   1-decyl-2-methyl dotriacontyl succinimide.

In another embodiment, R₁ and R₂ may be straight chain aliphatichydrocarbon groups. These friction modifiers have improved solubility inlubricating oil. Examples of these friction modifiers are:

-   1-methylpentadecyl succinimide-   1-propyltridecenyl succinimide-   1-pentyltridecenyl succinimide-   1-tridecylpentadecenyl succinimide-   1-tetradecyleicosenyl succinimide.

The above friction modifiers may be made from linear α-olefinscontaining about 12 to about 36 carbon atoms by isomerizing theα-olefins to form a mixture of internal olefins and reacting thismixture of internal olefins with maleic acid, anhydride or ester formingan intermediate and reacting the intermediate with ammonia to formamide, imide, or mixtures thereof. Friction modifiers made fromisomerized linear α-olefins have greatly improved oil solubilitycompared with friction modifiers made with linear α-olefins.

Isomerization of the linear α-olefin can be carried out usingconventional methods. One suitable method is to heat the linear α-olefinwith an acidic catalyst. Especially useful acid catalysts are thesulfonated styrene-divinylbenzene copolymers. Such catalysts arecommercially available and are conventionally used as cation exchangeresins. In the present method they are used in their acid form. Use ofsuch resins for isomerizing linear α-olefins is described in U.S. Pat.No. 4,108,889, incorporated herein by reference.

The compositions of the present invention may include mixtures of two ormore friction modifiers. For example, a mixture of one or moresuccinimide friction modifiers with one or more amine friction modifiersmay be employed.

The Phosphonate

The additive composition of the present disclosure may contain one ormore phosphonates having the formula:

wherein R¹ is an alkyl or alkenyl group containing about 12 to about 30carbon atoms and wherein R² and R³ are each independently hydrogen, analkyl, or an alkenyl group. As examples, suitable alkyl groups mayinclude methyl, ethyl, propyl, isopropyl, n-butyl, t-butyl, isobutyl, orany combination thereof. Examples of these phosphonates are dimethyltriacontylphosphonate, dimethyl triacontenylphosphonate, dimethyleicosylphosphonate, dimethyl hexadecylphosphonate, dimethylhexadecenylphosphonate, dimethyl tetracontenylphosphonate, dimethylhexacontylphosphonate, dimethyl dodecylphosphonate, dimethyldodecenylphosphonate, and the like.

In an embodiment R¹ is an alkyl or alkenyl group containing about 16 toabout 20 carbon atoms. Examples of these phosphonates are dimethylhexadecylphosphonate, dimethyl hexadecenylphosphonate, dimethyloctadecylphosphonate, dimethyl octadecenylphosphonate, dimethyleicosylphosphonate, and the like.

Suitable alkylphosphonate monoesters and processes for manufacturing thesame are described in US 2004-0230068.

The phosphonates are added to the lubricating composition in an amountwhich improves friction performance, such as an amount that improvessteel-on-steel friction, steel-on-paper friction, and/or synchronizationperformance. A suitable concentration may be from about 0.05 to about 3wt %. As a further example, a suitable concentration may be from about0.10 wt % to about 0.6 wt %.

Detergent

In some embodiments, the additive composition may also comprise adetergent. The detergent may comprise an overbased detergent, a borateddetergent, and/or a borated overbased detergent. The detergent maycomprise a sulfonate or a phenate. Further, the detergent may comprise acalcium-containing, a magnesium-containing, or a sodium-containingcompound. The detergent may comprise, for example, a calcium sulfonate,a magnesium sulfonate, a sodium sulfonate, and/or a calcium phenate. Forexample, a calcium sulfonate detergent may comprise from about 1.5 wt %to about 20 wt % calcium, or as a further example from about 12 wt % toabout 15 wt % calcium. Further, a calcium sulfonate detergent maycomprise a total base number (TBN) of from about 3 mgKOH/g to about 450mgKOH/g, as a further example of from about 250 mgKOH/g to about 400mgKOH/g, and as an even further example of from about 250 mgKOH/g toabout 350 mgKOH/g. A calcium phenate detergent may comprise from about2.5 wt % to about 8.5 wt % calcium, or for example about 5 wt % calcium.Further, a calcium phenate detergent may comprise a TBN of from about 50mgKOH/g to about 300 mgKOH/g, or for example, about 150 mgKOH/g.

Embodiments may contain alkali metal detergents and/or alkaline-earthmetal detergents in addition or in the alternative to the detergentsdescribed above. Suitable alkali and alkaline-earth metal detergents mayinclude oil-soluble neutral or overbased salts of alkali andalkaline-earth metals with one or more of the following acidicsubstances (or mixtures thereof): sulfonic acids, carboxylic acids,salicylic acids, alkyl phenols, and sulfurized alkyl phenols.

Oil-soluble neutral alkali and alkaline-earth metal-containingdetergents are those detergents that contain stoichiometricallyequivalent amounts of alkali and alkaline-earth metal in relation to theamount of acidic moieties present in the detergent. Thus, in general theneutral alkali and alkaline-earth metal detergents will have a lowbasicity when compared to their overbased counterparts. Methods ofpreparation of overbased alkali and alkaline-earth metal-containingdetergents are known in the art and there are numerous commerciallyavailable overbased detergents on the market.

The alkali and alkaline-earth metal detergents include, but are notlimited to, neutral and overbased sodium sulfonates, sodiumcarboxylates, sodium salicylates, sodium phenates, sulfurized sodiumphenates, calcium sulfonates, calcium carboxylates, calcium salicylates,calcium phenates, sulfurized calcium phenates, lithium sulfonates,lithium carboxylates, lithium salicylates, lithium phenates, sulfurizedlithium phenates, magnesium sulfonates, magnesium carboxylates,magnesium salicylates, magnesium phenates, sulfurized magnesiumphenates, potassium sulfonates, potassium carboxylates, potassiumsalicylates, potassium phenates, and sulfurized potassium phenates.

The additive composition may be combined with a base oil to provide apower transmitting fluid. Such a power transmitting fluid may comprise afinished fluid.

In another embodiment, an automatic transmission fluid, or a dual clutchtransmission fluid, may comprise an additive composition disclosedherein. The fluid may be suitable for an automated dual clutchtransmission such as a DCT that employs at least two wet clutches. In anembodiment, the transmission fluid may be used in a DCT does not includea torque converter.

In another embodiment, a method of increasing steel-on-steel friction,stabilizing steel-on-paper friction and/or delivering good synchronizerperformance may comprise lubricating a transmission with a lubricatingcomposition comprising a major amount of a base oil and an additivecomposition as described herein.

A lubricating fluid may include other additives, such as, for example,one or more of an antiwear agent; an antioxidant or an antioxidantsystem, such as an amine antioxidant or phenolic antioxidant; acorrosion inhibitor or a corrosion inhibitor system; a metaldeactivator; an anti-rust agent; one or more additional frictionmodifiers; a dye; a seal swell agent; an anti-foam agent; a surfactant;a viscosity index improver; a perfume or odor mask; and any suitablecombinations thereof.

Sulfur-Containing Components

In some embodiments, the additive composition may also comprise one ormore sulfur-containing components. For example, the additive compositionmay comprise a thiadiazole and/or a sulfurized fatty acid ester.

Suitable thiadiazoles include dialkyl thiadiazoles, including but notlimited to an ashless dialkyl thiadiazole. Dialkyl thiadiazoles suitablefor the practice of the present invention may be of the general formula(I):

wherein R₁ and R₂ may be the same or different hydrocarbyl groups,and/or one of R₁ and R₂ may be hydrogen, and x and y independently maybe integers from 0 to 8. In one aspect, R₁ and R₂ may be the same ordifferent, linear, branched, or aromatic, saturated or unsaturatedhydrocarbyl group having from about 6 to about 18 carbon atoms,particularly from about 8 to about 12 carbon atoms, and x and y each maybe 0 or 1.

Suitable dialkyl thiadiazoles include2,5-bis(hydrocarbyldithio)-1,3,4-thiadiazoles. Examples of othersuitable dialkyl thiadiazoles include, for example,2,5-bis(hydrocarbylthio)-1,3,4-thiadiazoles,2-(tert-hydrocarbyldithio)-5-mercapto-1,3,4-thiadiazoles, andbis-tert-dodecylthiothiadiazole.

Suitable dialkyl thiadiazoles also include those such as described inU.S. Pat. Nos. 2,719,125, 2,719,126, 3,087,932, 4,149,982, 4,591,645,and 6,528,458, and which descriptions are incorporated herein byreference. Mixtures of dialkyl thiadiazoles of formula (I) withmonoalkyl thiadiazoles may also be used within the scope of the presentinvention.

As used herein, the term “hydrocarbyl group” or “hydrocarbyl” is used inits ordinary sense, which is well-known to those skilled in the art.Specifically, it refers to a group having a carbon atom directlyattached to the remainder of a molecule and having a predominantlyhydrocarbon character. Examples of hydrocarbyl groups include:

(1) hydrocarbon substituents, that is, aliphatic (e.g., alkyl oralkenyl), alicyclic (e.g., cycloalkyl, cycloalkenyl) substituents, andaromatic-, aliphatic-, and alicyclic-substituted aromatic substituents,as well as cyclic substituents wherein the ring is completed throughanother portion of the molecule (e.g., two substituents together form analicyclic radical);

(2) substituted hydrocarbon substituents, that is, substituentscontaining non-hydrocarbon groups which, in the context of thedescription herein, do not alter the predominantly hydrocarbonsubstituent (e.g., halo (especially chloro and fluoro), hydroxy, alkoxy,mercapto, alkylmercapto, nitro, nitroso, and sulfoxy);

(3) hetero-substituents, that is, substituents which, while having apredominantly hydrocarbon character, in the context of this description,contain other than carbon in a ring or chain otherwise composed ofcarbon atoms. Hetero-atoms include sulfur, oxygen, nitrogen, andencompass substituents such as pyridyl, furyl, thienyl, and imidazolyl.In general, no more than two, or as a further example, no more than one,non-hydrocarbon substituent will be present for every ten carbon atomsin the hydrocarbyl group; typically, there will be no non-hydrocarbonsubstituent in the hydrocarbyl group.

Alternatively, sulfurized fatty acid esters such as linear C₁₄-C₁₈saturated or unsaturated chain monocarboxylic acid esters which arecross-linked by sulfur moieties in the forms of mono-, di- andpoly-sulfides, may be employed. The relative fraction of the differentsulfur bridges depends on reaction conditions and the relative amount ofsulfur employed. The details of sulfurization of fatty acids are foundin several references such as Organic Sulfur Compounds by L. Bateman andC. G. Moore, and Mechanism of Sulfur Reaction by W. A. Pryor. Oneexemplary material is sulfurized oleic acid with a sulfur concentrationof about 5 to about 15% of the total weight of the sulfurized oleic acidester, incorporated as the mono- and di-sulfides.

The amount of the thiadiazole or sulfurized fatty acid ester is selectedto add sulfur to the composition in the amount of about 0.0075 to about0.5 weight percent sulfur, based on the total weight of the composition.

Base Oils

Embodiments of the lubricating fluid may comprise a major amount of abase oil. Base or lubricating oils contemplated in preparing the powertransmission fluids of the present disclosure may be derived fromnatural lubricating oils, synthetic lubricating oils, and mixturesthereof. Further, the base oil may comprise any suitable base oil ormixture of base oils for a particular application.

In some embodiments, additives may be provided in an additive packageconcentrate. Further, some embodiments may comprise a diluent, e.g., adiluent oil. A diluent may be included to ease blending, solubilizing,and transporting the additive package. The diluent may be compatiblewith a base oil and/or the additive package. The diluent may be presentin any suitable amount in the concentrate. A suitable diluent maycomprise a process oil of lubricating viscosity.

The additive combinations can be incorporated in a wide variety of baseoils in effective amounts to provide suitable active ingredientconcentrations. The base oils not only can be hydrocarbon oils oflubricating viscosity derived from petroleum (or tar sands, coal, shale,etc.), but also can be natural oils of suitable viscosities such asrapeseed oil, etc., and synthetic oils such as hydrogenated polyolefinoils; poly-α-olefins (e.g., hydrogenated or unhydrogenated α-olefinoligomers such as hydrogenated poly-1-decene); alkyl esters ofdicarboxylic acids; complex esters of dicarboxylic acid, polyglycol andalcohol; alkyl esters of carbonic or phosphoric acids; polysilicones;fluorohydrocarbon oils; and mixtures of mineral, natural and/orsynthetic oils in any proportion. The term “base oil” for thisdisclosure includes all the foregoing.

The additive combinations can thus be used in compositions, in which thebase oil of lubricating viscosity is a mineral oil, a synthetic oil, anatural oil such as a vegetable oil, or a mixture thereof, e.g. amixture of a mineral oil and a synthetic oil.

Suitable mineral oils include those of appropriate viscosity refinedfrom crude oil of any source including Gulf Coast, Mid-continent,Pennsylvania, California, Alaska, Middle East, North Sea, and the like.Standard refinery operations may be used in processing the mineral oil.Among the general types of suitable petroleum oils are solvent neutrals,bright stocks, cylinder stocks, residual oils, hydrocracked base stocks,paraffin oils including pale oils, and solvent extracted naphthenicoils. Such oils and blends of them are produced by a number ofconventional techniques which are widely known by those skilled in theart.

As is noted above, the base oil can consist essentially of or comprise aportion of one or more synthetic oils. Among the suitable synthetic oilsare homo- and inter-polymers of about C₂ to about C₁₂ olefins,carboxylic acid esters of both monoalcohols and polyols, polyethers,silicones, polyglycols, silicates, alkylated aromatics, carbonates,thiocarbonates, orthoformates, phosphates and phosphites, borates andhalogenated hydrocarbons. Representative of such oils are homo- andinterpolymers of about C₂ to about C₁₂ monoolefinic hydrocarbons,alkylated benzenes (e.g., dodecyl benzenes, didodecyl benzenes,tetradecyl benzenes, dinonyl benzenes, di-(2-ethylhexyl)benzenes,wax-alkylated naphthalenes); and polyphenyls (e.g., biphenyls,terphenyls).

Alkylene oxide polymers and interpolymers and derivatives thereof wherethe terminal hydroxyl groups have been modified by esterification,etherification, and the like, constitute another class of syntheticoils. These are exemplified by the oils prepared through polymerizationof alkylene oxides such as ethylene oxide or propylene oxide, and thealkyl and aryl ethers of these polyoxyalkylene polymers (e.g., methylpolyisopropylene glycol ether having an average molecular weight ofabout 1000, diphenyl ether of polyethylene glycol having a molecularweight of about 500 to about 1000, diethyl ether of polypropylene glycolhaving a molecular weight of about 1000 to about 1500) or mono- andpoly-carboxylic esters thereof, for example, the acetic acid ester,mixed about C₃ to about C₆ fatty acid esters, or the C₁₃ Oxo aciddiester of tetraethylene glycol.

Another suitable class of synthetic oils comprises the esters ofdicarboxylic acids (e.g., phthalic acid, succinic acid, maleic acid,azelaic acid, suberic acid, sebacic acid, fumaric acid, adipic acid,linoleic acid dimer) with a variety of alcohols (e.g., butyl alcohol,hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol, ethylene glycol).Specific examples of these esters include dibutyl adipate,di(2-ethylhexyl)adipate, didodecyl adipate, di(2-ethylhexyl)sebacate,dilauryl sebacate, di-n-hexyl fumarate, dioctyl sebacate, diisooctylazelate, diisodecyl azelate, dioctyl phthalate, didecyl phthalate,di(eicosyl)sebacate, the 2-ethylhexyl diester of linoleic acid dimer,and the complex ester formed by reacting one mole of sebacic acid withtwo moles of tetraethylene glycol and two moles of 2-ethylhexanoic acid.

Esters which may be used as synthetic oils also include those made fromabout C₃ to about C₁₂ monocarboxylic acids and polyols and polyol etherssuch as neopentyl glycol, trimethylolpropane, pentaerythritol anddipentaerythritol. Trimethylol propane tripelargonate andpentaerythritol tetracaproate serve as examples.

Silicon-based oils such as the polyalkyl-, polyaryl-, polyalkoxy-, orpolyaryloxy-siloxane oils and silicate oils comprise another class ofsynthetic lubricants (e.g., tetraethyl silicate, tetraisopropylsilicate, tetra-(2-ethylhexyl) silicate, tetra-(p-tert-butylphenyl)silicate, poly(methyl)siloxanes, and poly(methylphenyl)siloxanes. Othersynthetic lubricating oils include liquid esters ofphosphorus-containing acids (e.g., tricresyl phosphate, trioctylphosphate, triphenyl phosphite, and diethyl ester of decane phosphonicacid.

Also useful as base oils or as components of base oils are hydrogenatedor unhydrogenated liquid oligomers of about C₆ to about C₁₆ α-olefins,such as hydrogenated or unhydrogenated oligomers formed from 1-decene.Methods for the production of such liquid oligomeric 1-alkenehydrocarbons are known and reported in the literature. See for exampleU.S. Pat. Nos. 3,749,560; 3,763,244; 3,780,128; 4,172,855; 4,218,330;and 4,950,822; the disclosures of which are incorporated herein byreference. Blends of such materials can also be used in order to adjustthe viscometrics of the given base oil. As is well known, hydrogenatedoligomers of this type contain little, if any, residual ethylenicunsaturation.

Suitable oligomers may be formed by use of a Friedel-Crafts catalyst(especially boron trifluoride promoted with water or a about C₁ to aboutC₂₀ alkanol) followed by catalytic hydrogenation of the oligomer soformed using procedures such as are described in the foregoing U.S.patents.

Other catalyst systems which can be used to form oligomers of 1-alkenehydrocarbons, which, on hydrogenation, provide suitable oleaginousliquids include Ziegler catalysts such as ethyl aluminum sesquichloridewith titanium tetrachloride, aluminum alkyl catalysts, chromium oxidecatalysts on silica or alumina supports and a system in which a borontrifluoride catalyst oligomerization is followed by treatment with anorganic peroxide.

It is also possible in accordance with this disclosure to utilize blendsof one or more liquid hydrogenated 1-alkene oligomers in combinationwith other oleaginous materials having suitable viscosities, providedthat the resultant blend has suitable compatibility and possesses thephysical properties desired.

The base oil may be an oil derived from Fischer-Tropsch synthesizedhydrocarbons, a gas-to-liquid stock, and/or a mixture thereof.Fischer-Tropsch synthesized hydrocarbons are made from synthesis gascontaining H₂ and CO using a Fischer-Tropsch catalyst. Such hydrocarbonstypically require further processing in order to be useful as the baseoil. For example, the hydrocarbons may be hydroisomerized usingprocesses disclosed in U.S. Pat. No. 6,103,099 or 6,180,575;hydrocracked and hydroisomerized using processes disclosed in U.S. Pat.No. 4,943,672 or 6,096,940; dewaxed using processes disclosed in U.S.Pat. No. 5,882,505; or hydroisomerized and dewaxed using processesdisclosed in U.S. Pat. No. 6,013,171; 6,080,301; or 6,165,949.

Typical natural oils that may be used as base oils or as components ofthe base oils include castor oil, olive oil, peanut oil, rapeseed oil,corn oil, sesame oil, cottonseed oil, soybean oil, sunflower oil,safflower oil, hemp oil, linseed oil, tung oil, oiticica oil, jojobaoil, and the like. Such oils may be partially or fully hydrogenated, ifdesired.

The fact that the base oils used in the compositions of this disclosuremay be composed of (i) one or more mineral oils, (ii) one or moresynthetic oils, (iii) one or more natural oils, or (iv) a blend of (i)and (ii), or (i) and (iii), or (ii) and (iii), or (i), (ii) and (iii)does not mean that these various types of oils are necessarilyequivalents of each other. Certain types of base oils may be used incertain compositions for the specific properties they possess such ashigh temperature stability, nonflammability or lack of corrosivitytowards specific metals (e.g. silver or cadmium). In other compositions,other types of base oils may be suitable for reasons of availability orlow cost. Thus, the skilled artisan will recognize that while thevarious types of base oils discussed above may be used in the variousembodiments, they are not necessarily functional equivalents of eachother in every instance.

The Method of Use

The additive compositions and/or lubricating fluids of the presentdisclosure may be employed in a method for lubricating an automatictransmission, and, more specifically, in a method for lubricating a DCT,such as, a DCT that utilizes plural wet clutches and no torqueconverter.

The method of the present disclosure involves lubricating a transmissionwith a lubricating fluid comprising:

-   -   (a) an ashless dispersant;    -   (b) a friction-modifying amount of a friction modifier; and    -   (c) a phosphonate.        The fluid is substantially zinc-free and may deliver improved        steel-on-steel friction, stabilized steel-on-paper friction        and/or good synchronizer performance.

EXAMPLES

Fluids for testing were prepared in targeted basestocks. The fullyformulated fluids were prepared by adding components together inproportions shown below: TABLE 1 Antiwear/Extreme Pressure 0.05-1.0%Agents Antioxidants  0.1-0.6% Rust Inhibitors 0.01-0.2% DMOP 0.10-0.6%Antifoam agents 0.01-0.1% Friction Modifier  0.3-1.0% Dispersant A  1-6%Seal Swell Agents  0-10% Polymethacrylate VII  3-25% Basestock  60-90%Diluent Oil  2-5%Dispersants used are succinimide dispersants that may or may not containboron and/or phosphorus. The friction modifier was a succinimide havinga C₁₈-C₂₄ alkenyl group. DMOP is dimethyl octadecylphosphonate.Additional friction modifiers may be used to tailor frictionrequirements.

Dispersant and friction modifiers provide appropriate torque capacity.Fluid compositions containing dispersant and succinimide frictionmodifiers have been developed to provide good friction durability. FIG.1 is a comparison of the friction characteristics of Fluid A (Table 2)containing succinimide dispersant and succinimide friction modifier withfriction characteristics before and after thermal aging.

Thermal aging was carried out by heating the fluid in a round bottomedflask equipped with a mechanical stirrer at 160° C. for 192 hours. Itmay be seen that the fluid is able to withstand thermal stress as thethermally stressed fluid displays good friction durability and maintainsboth friction level and slope characteristics that are comparable tofresh fluid. TABLE 2 Composition of Fluid A Component Amount, wt %Antioxidant 0.1-0.5 Detergent 0.1-0.6 Rust Inhibitor(s)   0-0.2Antiwear/Extreme Pressure Agent 0.05-1.0  Lubricity Agent(s) 0.1-1.0Anti-foam Agent(s) 0.02-1.0  Amine Friction Modifier 1 0.02-0.15 AmineFriction Modifier 2 0.02-0.1  Succinimide Friction Modifier 0.1-0.8Borated, Phosphorylated Succinimide Dispersant 2.00-7.5  EthoxylatedAlcohol 0.01-0.5  Process Oil 0.10-1.50 Base Oil to 100% Total 100.0

The detergent employed in the composition was an overbased C₁₄-C₂₄α-olefin calcium sulfonate detergent. The friction modifier was asuccinimide having a C₁₈-C₂₄ alkenyl group. DMOP is dimethyloctadecylphosphonate. The friction modifier in combination with DMOPgives excellent synchronizer performance.

A matrix of fluids (Table 3) comprising two types of antiwear,dispersant, friction modifier and basestock showed that the samefriction modifier/DMOP combination in a synthetic fluid can giveexcellent synchronizer performance giving 100,000 cycles in the SSP-180synchronizer test using brass cones.

The SSP-180 test stand was developed in the Gear Research Institute atthe Technical University of Munich. It allows mounting and testing of acomplete synchronizer device (up to 180 mm in diameter) from a manualtransmission of choice. Load conditions associated with normaltransmission use are simulated during the test. The test stand consistsof an electric motor, two flywheels, actuating hydraulics, an oilheating and circulation system, and a test box. The large main flywheelis connected to the electric motor via a belt-and-pulley combination toensure a constant and stable speed source. The small flywheel is theload that the synchronizers either bring to zero speed (shift to “A”position) or accelerate to a constant speed (shift to “B” position).This is accomplished by the two ring-and-cone synchronizers mounted inthe test box. The rear unit accelerates the load flywheel to synchronousspeed, while the forward unit decelerates the flywheel to zero speed.The actuating hydraulics move a shift fork that engages one unit anddisengages the other. During shifting, heated lubricant is sprayed ontoboth synchronizer units. Subjecting these units to thousands ofengagements serves to test synchronizer durability (adapted fromhttp://www.swri.org/3PUBS/BROCHURE) TABLE 3 Synchronizer Performance ofFluids containing Friction Modifier/DMOP Matrix 1 2 3 4 5 6 7 8 Base OilSynthetic Mineral Mineral Synthetic Synthetic Mineral Synthetic MineralGO- 1100 1200 1300 1400 1500 1600 1700 1800 10631- AW ZDDP PhosphorousZDDP ZDDP Phosphorous ZDDP Phosphorous Phosphorous Acid Acid Acid AcidAW Level 1500 1500 1500 300 1500 300 300 300 Dispersant SuccinimideBorated Borated Borated Succinimide Succinimide Borated SuccinimideDispersant Succinimide Succinimide Succinimide Dispersant DispersantSuccinimide Dispersant Dispersant Dispersant Dispersant DispersantDispersant 0.5 0.5 5 5 5 0.5 0.5 5 level Detergent 1.5 1.5 0.35 1.5 0.350.35 0.35 1.5 level Ethoxylated Ethoxylated Ethoxylated AmineSuccinimide Succinimide Succinimide Succinimide Amine Amine FrictionFriction Friction Friction Friction Friction Friction FM type ModifierModifier + DMOP ATF Modifier + Modifier + Modifier + Modifier ModifierDMOP DMOP DMOP Base Oil Synthetic Mineral Mineral Synthetic SyntheticMineral Synthetic Mineral Cycles 83,278 67,077 21,157 100,000 100,000100,000 49,327 43,867 Avg 0.785 1.0565 1.17 0.615 0.3565 0.4365 0.9750.995 Wear High 1.107 1.1 1.1785 0.72 0.437 0.49 1.06 1.28 Wear Avg0.093 0.077 0.08 0.0875 0.109 0.0945 0.0815 0.098 COF Low 0.084 0.0640.068 0.084 0.106 0.094 0.066 0.09 COF Avg Sp 0.094 0.158 0.553 0.0620.036 0.044 0.198 0.227 Wear Max Sp 0.133 0.151 0.561 0.072 0.044 0.0490.215 0.292 Wear

In addition to contributing to good synchronizer performance andantiwear protection in the synchronizer test, DMOP also providedexcellent extreme pressure performance as measured using the Falex EP(Extreme Pressure) and 4-Ball EP tests according to ASTM D-3233 andD-2783 respectively. ASTM D-3233 performance is measured by determiningthe threshold load at which the test surfaces seize due to the appliedload at a given temperature. ASTM D-2783 measures the Weld point of asteel ball rotated against 3 stationary balls. Table 4 shows improvedperformance at 0.25% of DMOP compared to a similar composition withoutDMOP. TABLE 4 Falex EP D-3233 Falex EP D-3233 Fail load (lbs) Fail load(lbs) 4-Ball EP DMOP (wt. %) @ 100° C. @ 150° C. ASTM D-2783 0.25 21252000 260 Kg Weld 0.00 1250 1000 210 Kg Weld

As used throughout the specification and claims, “a” and/or “an” mayrefer to one or more than one. Unless otherwise indicated, all numbersexpressing quantities of ingredients, properties such as molecularweight, percent, ratio, reaction conditions, and so forth used in thespecification and claims are to be understood as being modified in allinstances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the specification andclaims are approximations that may vary depending upon the desiredproperties sought to be obtained by the present disclosure. At the veryleast, and not as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, each numerical parameter shouldat least be construed in light of the number of reported significantdigits and by applying ordinary rounding techniques. Notwithstandingthat the numerical ranges and parameters setting forth the broad scopeof the disclosure are approximations, the numerical values set forth inthe specific examples are reported as precisely as possible. Anynumerical value, however, inherently contains certain errors necessarilyresulting from the standard deviation found in their respective testingmeasurements.

While the present disclosure has been described in some detail by way ofillustration and example, it should be understood that the embodimentsare susceptible to various modifications and alternative forms, and arenot restricted to the specific embodiments set forth. It should beunderstood that these specific embodiments are not intended to limit theinvention but, on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention.

1. A method of lubricating a dual clutch transmission with a lubricatingfluid comprising the step of lubricating a dual clutch transmission witha substantially zinc-free lubricating fluid comprising: (a) an ashlessdispersant; (b) a friction modifier; (c) a phosphonate; and (d) a baseoil.
 2. The method of claim 1, wherein the base oil comprises a naturallubricating oil, a mixture of natural lubricating oils, a synthetic oil,a mixture of synthetic oils, or a mixture of natural and synthetic oils.3. The method of claim 1, wherein the dispersant comprises boron.
 4. Themethod of claim 3, wherein the boron-containing dispersant comprisesfrom about 0.1 wt % to about 0.7 wt % of boron.
 5. The method of claim1, wherein the dispersant comprises phosphorous.
 6. The method of claim1, wherein the dispersant comprises phosphorous and boron.
 7. The methodof claim 6, wherein the dispersant comprises up to about 400 ppm totalphosphorous and boron.
 8. The method of claim 1, wherein the phosphonateis selected from the group consisting of phosphonates having theformula:

wherein R¹ is an alkyl or alkenyl group containing about 12 to about 30carbon atoms and wherein R² and R³ are each independently hydrogen, analkyl, or an alkenyl group.
 9. The method of claim 8, wherein thephosphonate is selected from the group consisting of dimethyltriacontylphosphonate, dimethyl triacontenylphosphonate, dimethyleicosylphosphonate, dimethyl hexadecylphosphonate, dimethylhexadecenylphosphonate, dimethyl tetracontenylphosphonate, dimethylhexacontylphosphonate, dimethyl dodecylphosphonate, dimethyldodecenylphosphonate, dimethyl hexadecylphosphonate, dimethylhexadecenylphosphonate, dimethyl octadecylphosphonate, dimethyloctadecenylphosphonate, and dimethyl eicosylphosphonate.
 10. The methodof claim 8, wherein the phosphonate is selected from the groupconsisting of phosphonates wherein R¹ is an alkyl or alkenyl groupcontaining about 16-20 carbon atoms.
 11. The method of claim 8, whereinthe phosphonate comprises dimethyl octadecylphosphonate
 12. The methodof claim 1, wherein the lubricating composition comprises from about0.05 to about 3 wt % of the phosphonate, based on the total weight ofthe lubricating composition.
 13. The method of claim 1, wherein theshifting of gears in the dual clutch transmission comprisessynchronization of an engaged and a non-engaged partial transmissionshaft.
 14. The method of claim 1, wherein the lubricating fluid furthercomprises at least one sulfur-containing compound.
 15. A dual clutchtransmission fluid comprising: (a) an ashless dispersant; (b) a frictionmodifier; (c) a phosphonate; and (d) a base oil, wherein the dual clutchtransmission fluid is substantially zinc-free.
 16. The transmissionfluid of claim 15, wherein the base oil comprises a natural lubricatingoil, a mixture of natural lubricating oils, a synthetic oil, a mixtureof synthetic oils, or a mixture of natural and synthetic oils.
 17. Thetransmission fluid of claim 15, wherein the dispersant comprises boron.18. The transmission fluid of claim 17, wherein the boron-containingdispersant comprises from about 0.1 wt % to about 0.7 wt % of boron. 19.The transmission fluid of claim 15, wherein the dispersant comprisesphosphorous.
 20. The transmission fluid of claim 15, wherein thedispersant comprises phosphorous and boron.
 21. The transmission fluidof claim 20, wherein the dispersant comprises up to about 400 ppm totalphosphorous and boron.
 22. The transmission fluid of claim 15, whereinthe phosphonate is selected from the group consisting of phosphonateshaving the formula:

wherein R¹ is an alkyl or alkenyl group containing about 12 to about 30carbon atoms and wherein R² and R³ are each independently hydrogen, analkyl, or an alkenyl group.
 23. The transmission fluid of claim 22,wherein the phosphonate is selected from the group consisting ofdimethyl triacontylphosphonate, dimethyl triacontenylphosphonate,dimethyl eicosylphosphonate, dimethyl hexadecylphosphonate, dimethylhexadecenylphosphonate, dimethyl tetracontenylphosphonate, dimethylhexacontylphosphonate, dimethyl dodecylphosphonate, dimethyldodecenylphosphonate, dimethyl hexadecylphosphonate, dimethylhexadecenylphosphonate, dimethyl octadecylphosphonate, dimethyloctadecenylphosphonate, and dimethyl eicosylphosphonate.
 24. Thetransmission fluid of claim 22, wherein the phosphonate is selected fromthe group consisting of phosphonates wherein R¹ is an alkyl or alkenylgroup containing about 16-20 carbon atoms.
 25. The transmission fluid ofclaim 22, wherein the phosphonate comprises dimethyloctadecylphosphonate
 26. The transmission fluid of claim 15, wherein thelubricating composition comprises from about 0.05 to about 3 wt % of thephosphonate, based on the total weight of the lubricating composition.27. The transmission fluid of claim 15, wherein the lubricatingcomposition further comprising at least one sulfur-containing compound.